Investigators have also uncovered a vital detail they can use to prove whether they’ve found the killer when an arrest is made. For obvious reasons, they did not reveal what it was. As to the other cases, police records show an 18-year-old woman was fondled as she entered her Inwood building in March, and a 41-year-old woman was groped in the lobby of her Washington Heights building.

The attacker was a heavyset man in his 20s.

A third case involved a man who grabbed a woman by the throat in Fort Washington Park last October.

A month later, a Parks Department worker was accosted in Central Park’s Harlem Meer by a man in his 20s.

Investigators have concluded that Fox’s killer didn’t move her body far from where she was strangled on May 19 as she jogged inside Inwood Hill Park. The killer carefully placed 24 blossoms from a tulip tree in a circle around her, investigators confirmed to The Post.

In another bizarre case, a man who lives at 108th Street and Park Avenue told cops he jogged inside Inwood Hill Park every day and saw a man carrying the naked body of a white woman and clothing in a green plastic grocery bag.

But that story fell apart when he couldn’t answer how he traveled to the park each day.

The case is proving to be the toughest yet for grizzled veteran homicide detective Robert Mooney, leading the hunt for Fox’s killer.

Mooney, 47, is no stranger to solving high-profile crimes.

In 2000 he helped nab serial killer Aaron Kee by tricking him into leaving a DNA sample on a coffee cup and secured the conviction in the murder of a Columbia University coed.

In 2001, he cracked the case of a 37-year-old man who used a dog leash to strangle an 81-year-old Harlem socialite and later conducted the gruesome task of identifying 9/11 victims from body parts.

Meanwhile, the NYPD is offering a $10,000 reward for information on the case and is urging tipsters to call (800) 577-TIPS. (p. 19 Metro)